[The isolation and phenotypic characteristics of heat-resistant cells from the Chinese hamster CHO-K1 line]. / Poluchenie i fenotipicheskie osobennosti termorezistentnykh kletok kitaiskogo khomiachka linii CHO-K1.

By sequential selection for a resistance to a short-term heating at 45 degrees C, two independent clones, CHSR5 and CHSR6, have been isolated from ovarian cells of the Chinese hamster (CHO-K1). A subline CHO-A40, capable of proliferation at 40 degrees C, has been obtained as mass culture by culturing CHO-K1 cells for 2 months at 40 degrees C. The lines obtained have no cross-resistance to the temperature used in their selection: the CHSR5 and CHSR6 cells are not capable of reproduction at 40 degrees C, while the CHO cells do not survive over a 60 min heating at 45 degrees C. This bears evidence that mechanisms, underlying the cell resistance under different thermal regimens used, may be different. The heat resistant sublines maintain their heat resistance for 6 months of cultivation at 37 degrees C. The acquisition of heat resistance by cells correlates with their high primary resistance, and with their resistance to colchicine and actinomycin D.

[The protein spectrum and thermostability of the lysosomal hydrolases in heat-resistant sublines of Chinese hamster cells]. / Izuchenie spektra belkov i teploustoichivosti lizosomal'nykh gidrolaz v termorezistentnykh subliniiakh kletok kitaiskogo khomiachka.

It has been shown by electrophoresis that the earlier obtained thermoresistant sublines of the CHO-K1 cell line do not accumulate heat shock proteins when cultured at 37 degrees C. The thermostability of two lysosomal proteins--acid lipase and acid phosphatase--were higher in the thermoresistant cells than in the parental cells, whereas no differences in thermostability of galactosidase were found between heat resistant and parental lines. Thus, it is concluded that changes in the level of conformational flexibility of protein molecules may be one of the mechanisms of cell adaptation to growth at higher temperatures.

[The temperature dependence of protein kinase A and C activity in variant mouse neuroblastoma cells differing genetically in their heat resistance]. / Temperaturnaia zavisimost' aktivnosti proteinkinaz A i C u variantov kletok neiroblastomy myshi, geneticheski razlichaiushchikhsia po teploustoichivosti.

The ability of the mouse neuroblastoma cell line NTR to proliferate at 40 degrees C correlates with the position of the temperature optimum of protein kinases A and C activities in the region of higher temperatures compared to those for cells of the original line N18AI, and with higher thermostability of protein kinase A after its heating at various elevated temperatures. The found changes in protein kinases A and C in the cells of NTR line mean that the selection of variants, capable of growing at elevated temperatures, is accompanied with conformational protein changes.

[General and primary thermoresistance in genetically differing variants of murine neuroblastoma]. / Obshchaia i pervichnaia teploustoichivost' u geneticheski razlichaiushchikhsia variantov neiroblastomy myshi.

General and primary thermoresistance of mouse neuroblastoma clonal cell lines derived from N18A subline was studied: the N18A1 clonal cell line was not treated by heat, the NTR1 was obtained by one-step selection for resistance to the long action of the temperature 40 degrees C, the NHSR1 was obtained by multistep selection for resistance to short-time treatment at 44 degrees C. The NHSR1 clonal line was shown to have higher general and primary thermoresistance by comparison with that of N18A1 cells. The NTR1 cell line, capable of unlimited proliferation at 40 degrees C, did not differ in general resistance but displayed a slower primary resistance compared to that in the N18A1 cells. Cells of all the three clones were found to be capable of temporary increasing in primary thermoresistance, i.e. hardening. A possible contribution of the primary resistance into the general one in cells of all the selected clones has been discussed.

[Changes in primary heat sensitivity of rhabdomyosarcoma PA-2 cells in rats during selection for heat resistance]. / Izmenenie pervichnoi termoustoichivosti kletok rabdomiosarkomy PA-2 krys v protsesse selektsii na termorezistentnost'.

Using the technique of multistep selection, a thermoresistant substrain (TR RA-2T45) was obtained from a rhabdomyosarcoma RA-2 strain. The cells of this substrain retain the ability to form lung metastasis after a 20 minute treatment at 45 degrees C in vitro. The selection of cells for their ability to retain their reproduction activity is accompanied by the increase in their primary thermoresistance. The increased reproductive thermoresistance and primary thermoresistance of the selected cells is hereditary stabilized. Cells of both original strain and its substrain are capable of thermal tolerance, which makes perspective the selection for further increase in thermoresistance in RA-2T4t cell population.